The class of polymers of carbon monoxide and olefin(s) has been known for some time. Brubaker, U.S. Pat. No. 2,495,286, produced such polymers of relatively low carbon monoxide content in the presence of free radical initiators, e.g., peroxy compounds. U.K. 1,081,304 produced similar polymers of higher carbon monoxide content in the presence of alkylphosphine complexes of palladium as catalyst. Nozaki extended the reaction to produce linear alternating polymers in the presence of arylphosphine complexes of palladium moieties and certain inert solvents. See, for example, U.S. Pat. No. 3,694,412.
More recently, the class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon has become of greater interest in part because of the greater availability of the polymers. The more recent processes for the production of these polymers, now becoming known as polyketones or polyketone polymers, are illustrated by a number of published European Patent Applications including 121,965, 181,014, 213,671 and 257,663. The process, now considered to be broadly conventional, generally involves the use of a catalyst composition formed from a compound of a Group VIlI metal selected from palladium, cobalt or nickel, the anion of a non-hydrohalogenic acid having a pKa below about 6 and preferably below 2, and a bidentate ligand of phosphorus, arsenic or antimony. The resulting polyketone polymers are relatively high molecular weight thermoplastics having established utility in the production of shaped articles by the methods which are conventional for thermoplastic polymers.
The process of producing the polyketone polymers typically involves contacting the carbon monoxide and ethylene hydrocarbon(s) under polymerization conditions in the presence of the catalyst composition and a reaction diluent in which the catalyst composition is soluble but in which the polyketone polymer product is relatively insoluble. In theory, this procedure should allow recycle of the liquid portion of the polyketone polymer product mixture containing the catalyst composition subsequent to removal of the insoluble polyketone polymer by filtration, decantation or other conventional procedures. However, in practice the situation regarding recycle is more complex. A portion of the catalyst composition, and in some instances a substantial portion, is occluded within the polymeric product and the resulting liquid portion of the product mixture is accordingly at least somewhat depleted in catalyst composition, particularly the palladium component. In such instances, the liquid portion, if recycled, would not efficiently function as a polymerization medium without the provision of additional catalyst composition. In addition, in all instances, the polymerization produces a certain amount of low molecular weight oligomer but in some instances the oligomer production is substantial. These oligomers are often soluble in the reaction diluent and recycle of the liquid portion of such a product mixture would lead to the undesirable build-up of oligomer. As a result of these difficulties, the liquid product of the production of the polyketone polymers is typically recovered and separated by distillation into a distillate comprising reaction diluent and a residue comprising the catalyst components and the oligomers. This catalyst-containing residue is decomposed if desired to obtain palladium useful in the production of new catalyst composition components. It would be of advantage to provide an improved process for the production of the polyketone polymers in which the liquid portion of a product mixture could be directly recycled for use in the subsequent polymerization.